HARRISBURG, Pa. -- An obscure state agency is blocking the implementation of new restrictions on mercury pollution by refusing to print the rule in a record of administrative actions.

The Legislative Reference Bureau has sided with opponents of Gov. Ed Rendell's proposed rule and says it will not publish the text in the Pennsylvania Bulletin. Publication puts an administrative rule into effect.

Rendell has sought to force the state's coal-fired power plants to cut mercury pollution by 90 percent by 2015. If it becomes official, Pennsylvania would become the nation's largest coal-mining and coal-burning state to approve a tougher-than-federal rule.

Once fully enforced, the rule could transform Pennsylvania from one of the biggest sources of mercury pollution into one of the cleaner coal-burning states. The state's 36 coal-fired plants send roughly five tons of mercury into the air each year.

Attorney General Tom Corbett's office certified the rule Dec. 29, after which the Rendell administration sought to publish it in the bulletin.

The state Senate voted last June to adopt the federal government's less strict mercury rule, and insists that it still has time to review the governor's proposal. But the governor's administration says that review period expired Nov. 30.

"We believe the regulations should be posted and that the Legislative Reference Bureau has overstepped ... the scope of its authority by not posting them," press secretary Kate Philips said Monday.

The bureau's director, Robert W. Zech Jr., would say only that his agency is drafting a response to a request Thursday by a Rendell lawyer that it publish the rule.

Opponents of the tougher rule say it could force some older coal-fired power plants out of business, costing jobs and pushing up electricity bills.

Smokestack mercury accumulates near power plants, working its way up through the food chain, accumulating in plants, fish and humans, state officials say. Children and fetuses are particularly vulnerable to effects of the toxic metal, which can damage the development of the nervous system, according to the Environmental Protection Agency.